Alkylated phenols, such as those which are sterically hindered, are widely used as stabilizers, as they inhibit, for example, oxidative and thermal degradation of a wide range of polymeric systems. These stabilizers are, for example, employed in an amount of about 0.01 to about 5% by weight, preferably about 0.01 to about 0.05% by weight, based upon the stabilized mixture. The levels of stabilizers in the polymer may vary considerably depending on the particular end use application, the degree of protection against degradation, variations in substrate, and the presence of synergizing stabilizers such as thermal stabilizers or ultraviolet light absorbers, and dyes or pigments. The stabilized polymer compositions are prepared by a number of means, for example, by mixing into thermoplastic substrates, or by dissolving in a co-solvent and mixing into a substrate solution. Many process variants for the manufacture of corresponding phenols having antioxidative properties have been developed. However, impurities, such as quinones, adversely effect the stability and, hence, the quality of the alkylated phenols. Accordingly, there are intensive efforts in the art to develop purification processes to avoid these disadvantages.
U.S. Pat. No. 4,386,224 relates to a method for stabilizing color and for reducing color of monoalkyl phenol compositions by addition of N,N-diethylhydroxylamine.
U.S. Pat. No. 3,285,855 describes the manufacture of alkylated phenols containing an alkyl ester group which can be used for the stabilization of synthetic organic polymers against oxidative degradation.
U.S. Pat. No. 4,316,996 discloses a process for the manufacture of phenolic antioxidants as well as a method of purifying the resulting phenols. The purification step first provides the neutralization of the used catalyst by addition of an aqueous base (e.g. Na.sub.2 CO.sub.3) and an alkyl substituted hydroxylamine and then, in a next step, the addition of an oxime and an alkyl substituted hydroxylamine. No granulation process is disclosed.
There is a strong ned for using granules of antioxidative alkylated phenols in the manufacture of polymers, such as polybutadienes, polyvinylchlorides and polystyrenes, since crystallized products are not sufficiently suitable for the corresponding application of the phenols. Furthermore, the handling of the granules is more convenient in the application process of the phenols. U.S. Pat. No. 5,006,284 discloses the manufacture of granules of sterically hindered phenols having antioxidative activities by introducing the melt of the manufactured phenols into an aqueous solution of methanol and isolating the granules. However, if such granules are partially obtained in the form of dust, this may impose difficulties in packing, transportation and handling in the industrial process. Accordingly, there is still a desire to optimize the properties of the resulting granules, for example, in terms of further reducing the amount of dust in the granules and especially in the enhancement of the long term color stability of the alkylated phenols.